Process of forming a multifocal lens



June 2, 1953 S. T. SHEARD ET AL PROCESS OF FORMING A MULTIFOCAL LENS Filed Dec. 7, 1949 INVE NTOR SAMUEL. T. SHEARD Lows F. Rowa BY ATTORNEY Patented June 2, 1953 2,640,299

UNITED STATES OFFICE 2,640,299 PROCESS OF FORMING A MULTIFOCAL LEN Samuel T. Sheard, Sturbridge, Mass, and Louis F. Rowe, North Woodstock, 001111., assignors to American Optical Company, Southbridge, Masa, a -voluntary associa ion of Massachusetts Application December 7, 1949, Serial No. 131,634 3 filaims; (C1. 49-82.1)

invention relates to improvements in added power throughout the area of the high This ophthalmic lenses of the bifocal or multifocal index piece of glass; a type and has particular reference to the pro- 2. The controlling of the temperatures used vision of a novel method of making the same. thr ughout the cycle of fusion to insure against character, particularly of the type embodying a of the assembly; and

,7 3. The eliminationof interfacial bubbles or indices of refraction fused in edge to edge relaother defects due to thetrapping of air or gases the countersink of a major piece of glass, great proper bonding of the glasses throughout the difiiculty has been encountered in obtaining a interfaces of the glasses.

clear, continuous and true optical surface of re- High index glasses such as the commonly quired shape and one free from interfacial bubknown barium crown glasses when combined, bles or other defects. under heating conditions, with a lower index It has been the practice in the past to form glass such as the commonly known commercial the segment portion of lenses of this nature with crown glass tend to react to an evolution of sink in the mayor piece of glass with the said extremely dlfficlllt to obtain a high yield of related curvatures being such that after fusion, practical and usable lenses the curvature of the interface would be sub- Another factor which is of extreme importstantially that required to introduce the added ance and one of major consideration in overpower through the focal field lying within the coming the above defects is that, throughout area of the high index piece of glass. the ophthalmic field, provision is made in the the shape of the countersink curve and intimately the fact that it would require new computation bond therewit of related curvatures and the pI'OVISIOII of new It has been found that, because of the parcharts as well as a completely new set of curve ticular inherent characteristics of such glasses generating tools for producing said curves if the as were requiredm forming such bifocal or multiindices of refraction of these portions or these focal lenses, great d fi'iculty has been encountered lenses were altered or made difierent from those in obtaining the required high fusing qualities. Standard the trade, made I lmp atl e that There are v r l factors h h m t b care the indices of refraction of these respective parts fully controlled and consme ed m perform n bemamtamed to the established standards This y eld of practlcal and bl lenses in a practical manner by the mere change of s of th difijculties were; the index of refraction of the glasses whereby 1. That of controlling the curvature throuehdifierent fu in temperatures might be in dout the interfaces of the fused pieces of glass It is 1 0f the prin ip l objects, therefore, of

which, as stated above, controls, in part, the the present invention to provide glasses having melting points and a or multifocal prior newly controlled related novel process of making bifocal lenses therefrom whereby all of the above art defects will be overcome in a simple and efficient manner and with said glasses having the standardized indices of refraction of the prior art and retaining all of the advantages thereof. 4

Another object is to provide a novel process of forming a multifocal lens of the above character whereby a major portion of standardized optical crown glass having an index of refraction of approximately 1.523 and having the inherent melting point of such glasses is combined by fusion with a composite button embodying a minor portion of a new barium crown glass having the standard relatively high index of refraction of approximately 1.616 but having a melting point higher than that of the optical crown glass whereby substantially all of the above-mentioned prior art defects are eliminated.

Another object is to provide a novel process of forming lenses of the above character wherein the composite button is supported in spaced relation with the countersink of the major portion during fusion by a wedge or spacer of glass which is less responsive to heat than the major and filler pieces of glass but which melts at a temperature lower than that at which the high index piece of the composite button melts and in which the related positions of the pieces and the fusing temperatures and time cycles are so controlled as to cause said glasses to respond to the fusion temperatures in such manner that the filler piece will drop to the curve of the countersink prior to the softening of the segment or high index portion of the button and the glass wedge or spacer member will thereafter respond to said fusing temperature to permit the segment portion or high index glass to thereupon drop with a squeegee action into relatively intimate relation with the countersink curve and completely extrude air or other gases whereby the countersink curve will assume the preshaped curve formed on the segment portion and fusion will take place throughout the faces with the elimination of distortions, bubbles or other similar defects.

Referring to the drawings:

Fig. 1 is a front elevational bodying the invention;

Fig. 2 is a sectional view of said lens taken as on line 2-2 of Fig. 1 and looking in the direction indicated by the arrows;

Figs. 3, 4, and 5 are enlarged sectional views illustrating the various steps in the process of manufacture; and

Fig. 6 is a diagrammatic view illustrating one of the defects of the prior art methods of forming such lenses.

Referring to the drawings wherein like characters of reference designate like parts throughout the several views,'as an illustration of one embodiment of the invention, the lens, as shown view of a lens emand comprises a glass which constitutes the distance the lens and a index glass 8 which constitutes the reading field of the lens.

The reading field, in this instance, is of the commonly known three-quarter shape wherein the top portion of the segment is cut away along an upwardly arching curve B and is replaced by a melting point for the minor portion interminor piece of barium crown high a filler piece H of substantially the same glass as the major portion.

In the past, it has been a common practice to form a countersink 10 in the major portion 1 of the curvature required to control, in part, the added power desired of the finished lens. The filler piece H is edge-fused to the minor portion 8 along the abutting edges it! so that when the button which comprises the joined portions 8 and H is fused within the countersink, a continuous surface 13 of desired curvature may be formed on this side of the blank.

It has been common practice to use a low index optical crown glass for the major portion 1 and for the filler portion H each being of substantially the same glass composition and of a relatively high melting point and to use a high index barium crown glass having a relatively low As stated above, these glasses are of standardized indices of refraction in the ophthalmic art and the charted curves and surfacing tools throughout the according to these indices of refraction to give corrective powers desired. The index of refraction of the minor portion 8 and the countersink curve are such as to introduce the added power desired throughout the area of the reading field in accordance with standard practice.

In fusing the composite button in the countersink it. in the past, different attempts were made to so support the button and control the fusing temperatures that when fusion took place, proper bonding of the glasses throughout the interfaces thereof would result and the trapping of bubbles, interfacial distortions and other defects would be eliminated.

In view of the fact that the high index low melting barium crown glass of the segment portion 8 was the first to soften and melt under the action of heat during fusion, an attempt was made to support the portion l l of higher melting point in spaced relation with the countersink with a view to permitting air orother gases to escape from between the pieces of glass during fusion. In view of the fact that the barium crown could not be heated to a temperature wherein it would fiow too readily and that the major portion 1 and the filler portion H were of the same relatively high melting point, great diificulty was encountered, due to the limited temperature which could be used, in having the spacer member cause a gap to remain throughout the top of the segment. This gap, in many instances, was such that it could not be removed by the ultimate forming of the outer optical surface on the blank, as illustrated by the dot and dash line 13, as an excessive amount of glass was required to be removed with the result that the overall size of the reading field could not be properly controlled. It is quite obvious that the size of the reading field decreases as the outer surface of the lens is ground away and in order to remain Within the size limits required, the above defect was, in many instances, intolerable.

An attempt was made to place the spacer memher, as illustrated at Hi, at the lower edge of the low melting segment 8 with the opposite edge 15 of the filler portion H engaging the countersink curve Hi. This, however, introduced diffi culty for the higher melting point glasses 1 and H, at their area of contact, would start to adhere to each other with sufficient tenacity that these harder glasses would not bend or rock as 1 considerably more the lower melting dropped .to the curve of the countersink with commercial standard but, however, the said stantially the same curvature as the curve if! or slightly flatter or of longer radius.

or spacer M, in this particular-"instance, s formed the present instance are as The major, crown glass portion? and thefiller portion II have a Littleton approximately 1338". index glass-8 has a. approximately 1375 or spacer I4 is preferablylsuchas erablymore viscous glass at 1300 The temperature of fusing, in the presentinstance, lies between 1400" and 1450 F. depending upon the time cycle employed during said fusing.

It has been stated above that glass is ,very

surface v active and absorbs gases, moistures, 4 etc.

glasses or that of the above.

By ,forming the glasses withthe related controlled softening temperatures, aststated above,

it is v possible; to; preheat the. glasses after assemoff :these ,gases glasses whereuponithe i raising of thelten p eraun to a hi he d re w l @115 th m e e eration to take -;place i;

outwardlyfrom between said pieces'of glass by a squeegee action when the portion Hdropsto the countersink curve [0. During this move.- inent'the adjacent portion of the segment-8 will simultaneously move to j a related position such as illustrated in Fig. 4;. It is to be notedthat the :wedge i l, at this stage, has not permitted the portion 8 adjacent thereto to dr'op to the countersink.

p takes place during the dropping of the portion to the curve of the countersink.

the fact that the spacer or wedge 14 in its response to with the adjacent surface curvature of theclolm gases will .be automatically fiel Due to the fact that the glasses'land H are of substantially the same composition, index and With glasses having the above-related melting points; the final specific fusion temperature which successful resultsiaapproximately 1425 F. and thetimecycle of fusion is approximately'three minutes. .It is; to beunderstood, however, that if "the fusion temperature is lowered, the time cycle is increased propor- 500" or 600 for said preheating may be employed whereupon the preheating temperature may be run up to from 900 to 1000" F. and thence up tim t mpe atu e o twe n11,50 to' i 3d0' i'i 'li to drive off the gases and thence up to the ultimate temperature required for fusion.

It is pointed out that with the above related melting points of the glasses wherein the segment 8 has a higher melting point than the optical crown glasses of the major portions 1 and the filler portion H, and by supporting the said glasses in spaced assembled relation with each other as shown diagrammatically in Fig. 3 by a wedge M of glass controlled to respond to heat of a desired temperature, as specified above, and by controlling the temperature and time cycle of fusion with said glasses it has been possible to obtain a greatly increased yield of practical lenses. This is due to the elimination of distortion of the interfacial curve and the elimination of air bubbles or other defects which were so prevalent with prior art methods.

Although the filler portion i i has been referred to as being the same index of refraction as the major portion 1, it is to be understood that a filler portion of a slightly higher index of refraction or of an index of refraction intermediate that of the segment portion 8 and the major crown portion 1 might be employed in which case a trifocal lens could be formed, keeping in mind, of course, that the softening point of said portion H must be less than the softening temperature of the portion 8 and substantially that of the major portion 1 or only slightly higher than said major portion.

During the fusing operation, the assembly is supported on a suitable refractory I!) having its upper surface 20 shaped substantially to the adjacent curvature of the engaging surface of the major portion 1.

In completing the lens, asurface of the required prescriptive curvature, as illustrated by the dot and dash line 2 l is formed on the opposed side of the blank.

It is further to be understood, of course, that the engaging surfaces of the segment and countersink are thoroughly cleansed prior to fusion in order to avoid the existence of dirt, dust or other foreign matter.

Although glasses having certain given melting points have been set forth above, it is to be understood that glasses having melting points other than those called for may be used. It is essential, however, that substantially the same ratio and related differences be maintained and that the related indices of refraction be held to the established standards. It is quite obvious that the fusing temperatures and time cycles will be altered according to melting points of the particuiar glasses used.

It has been stated above that the index of refraction of the portion 8 in the particular example given is 1.616 but it is to be understood that the index of refraction of the portion 8 may be varied from 1.57 to 1.66 as desired depending upon the ultimate thickness of the final lens. When the index of refraction is varied, the curve of the countersink is accordingly varied in order to obtain the final added power desired.

From the foregoing description, it will be seen that novel and improved lenses and a new an improved process has been provided in accordance with the objects and advantages of the invention.

Although the novel features and process have been shown and described and are pointed out in the annexed claims, it will be understood that many changes may be made as to the glasses,

shown and described without departing from the spirit of the invention as expressed in the accom panying claims. Therefore, it is to be understood that all matters and process are to be interpreted as illustrative of the invention and are not to be construed in a limiting sense.

Having described our invention we claim:

1. In the process of forming a multifocal lens of the type embodying a main element of one index of refraction having a concave seat therein and a composite button embodying a piece of lens medium of a higher index of refraction than the main element fused to said seat, the steps comprising first edge-fusing the lens medium of high index of refraction with a filler piece of lens medium having a substantially lower index of refraction and lower softening point than said lens medium of high index of refraction to form a composite button, shaping the under surface of the button to a convex shape in accordance with the added power desired in the finished lens, forming a concaved seat in the upper surface of a main element of an index of refraction lower than the high index medium of the button and having a softening .point approaching that of said filler piece, resting an outer peripheral portion of the filler piece of said button on the edge of the concave seat in said upper surface of the main element and supporting the peripheral edge of the high index lens medium of the button off the edge of the concave seat by spacer means positioned between said high index lens medium and the edge of the concave seat, and under the action of heat causing first the filler piece to soften and drop into intimate relation with the seat and simultaneously carry the fused edge of the high index lens medium therewith and thereafter the remainder of the high index lens medium to drop onto said seat to cause said seat to assume the shape of the under-side of said high index lens medium and cause said composite button to fuse to said seat, said underside and fused edge of said high index lens medium remaining substantially unchanged during said dropping and fusing of the button to said seat.

2. In the process of forming a multifocal lens of the type embodying a main element of one index of refraction having a concave seat therein and a composite button embodying a piece of lens medium of a higher index of refraction than the main element fused to said seat, the steps comprising a first edge-fusing the lens medium of high index of refraction with a filler piece of lens medium having a substantially lower index of refraction and lower softening point than said lens medium of high index of refraction to form a composite button, shaping the under surface of the button to a convex shape in accordance with the added power desired in the finished lens, forming in the upper surface of a main element having an index of refraction and a softening point approaching that of said filler piece a concaved seat of relatively shallower curvature than that of the underside of the button, resting an outer peripheral portion of the filler piece of said button on the edge of the concave seat in said upper surface of the main element and supporting the peripheral edge of the high index lens medium of the button off the edge of the concave seat by spacer means positioned between said high index lens medium and the edge of the concave seat, and, under the action of heat, causing first into intimate relation with the seat and simulfu'sing temperatures and steps of the process taneously carry the fused edge of the high index lens medium therewith and thereafter the remainder of the high index medium to drop onto said seat to cause said seat to assume the shape of the underside of said high index lens medium. and cause said composite button to fuse to said seat, said underside and fused edge of said high index lens medium remaining substantially unchanged during said dropping and fusing of the button to the seat.

3. In the process of forming a multifocal lens of the type embodying a main element of one index of refraction having a concave seat therein and a composite button embodying a .piece of lens medium of a higher index of refraction than the main element fused to said seat, the steps comprising first edge-fusing the lens medium of high index of refraction with a filler piece of lens medium having a substantially lower index of refraction and lower softening point than said lens medium of high index of refraction to form a composite button, shaping the under surface of the button to a convex shape in accordance with the added power desired in the finished lens, forming a concaved seat in the upper surface of a main element of an index of refraction lower than the high index medium of the button and having a softening .point approaching that of said filler piece, resting an outer peripheral portion of the filler piece of said button on the edge of the concave seat in said upper surface of the main element and supporting the peripheral edge of the high index lens medium of the button off the edge of the concave seat by spacer means positioned between said high index lens medium and the edge of the concave seat, said spacer means having a softening point intermediate that of the filler piece and the high index lens medium of the button and under the action of heat causing first the filler piece to soften and drop into intimate relation with the seat and simultaneously carry the fused edge of the high index lens medium therewith and thereafter the spacer means to soften and allow the remainder of the high index lens medium to drop onto said seat causing said seat to assume the shape of the under-side of said high index lens medium and said composite button to fuse to said seat, said underside and fused edge of said high index lens medium remaining substantially unchanged during said dropping and fusing of the button to said seat.

SAMUEL T. SHEAR-D. LOUIS F. ROWE,

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